LONDON — Even Michael Phelps seemed to see the night for what it was: a good-bye party for him and a hello to a new generation. It was a rare night when Phelps swam, dominated and even made a little history yet was not the biggest story line. He might not have even been the second-biggest story line, for that matter.

Two teenage girls — one from Bethesda — stole that distinction.

More impressive than Phelps’s victory in the 100-meter butterfly in 51.21 seconds over South African Chad le Clos and Russian Evgeny Korotyshkin, who tied for second in 51.44?

How about the utter domination of Missy Franklin, 17, in the 200-meter backstroke, an event in which she broke the world record and defeated the second-place finisher by nearly two seconds?

Or the gold-medal performance by Stone Ridge’s Katie Ledecky, who in her first major international event led the 800-meter freestyle from start to finish and came within a second of breaking the four-year-old world record in the event?

“The sport is going to be fun to watch,” said Phelps, who will compete in his final event, the 4x100 medley relay, Saturday night. “I’m excited to see it from the outside more than anything, what these young people are going to do to continue to change the sport.”

Franklin beamed after touching the wall in 2 minutes, 4.06 seconds, easily sliding under the previous world best of Zimbabwe’s Kirsty Coventry, 2:04.81, set during the Supersuit era in Rome in 2009. She topped Russian Anastasia Zueva (2:05.92) and U.S. teammate Elizabeth Beisel (2:06.55).

Franklin, who has won three gold medals and one bronze in her first Olympics, has one more chance for a medal in Saturday’s 4x100 medley relay.

“I just wanted to go out and do my best and get a best time,” she said. “My best time just happened to be a world record.”

Ho-hum, sometimes that happens.

Franklin seems like a seasoned veteran compared to Ledecky, 15, whose competition here began in Thursday’s preliminary round and ended when she touched the wall in 8:14.63, breaking the American record held by distance legend Janet Evans.

She beat Spain’s Mireia Garcia Belmonte, who finished in 8:18.76, and Britain’s Rebecca Adlington, the reigning Olympic champion who came home in 8:20.32. Adlington was supported by a roaring, flag-waving crowd. Ledecky got a good luck from Phelps, and felt the cheers of her parents, brother and several relatives wearing Team Ledecky T-shirts — even if she couldn’t quite hear them amid all of the “Becky! Becky!” chants.

“I was a lot more calm than I was for the preliminary swim,” Ledecky said. “I just used the crowd. I put all that energy into the race.”

A year ago, the biggest meet of Ledecky’s summer was the U.S. junior national championships, where she won three gold medals. Friday, the stage was a little bigger.

Said Donna de Varona, who won two gold medals at the 1964 Olympics and watched from the stands: “I haven’t seen a better women’s team since . . . I can’t even tell you when. That says a lot.”

It was a great night all around for the United States. To top it off, Cullen Jones grabbed the silver in the 50 freestyle, finishing in 21.54 as Frenchman Florent Manaudou got first in 21.34. American Anthony Ervin, who won the gold medal in the event 12 years ago at the 2000 Summer Games, got fifth in 21.78.

“I’m thankful that I got second,” Jones said.

For his part, Phelps seemed to put a good part of his energy into enjoying the moment. As he did Thursday in winning the 200 individual medley, he produced an Olympic three-peat, he captured his third consecutive Olympic title with his victory. And he did it without the drama of the 2008 Games, when he came from behind and slipped his hand on the wall at the last moment, beating Serbian Milorad Cavic by just .01 seconds.

The King of his Sport, his Olympic medals record total now up to 21, has been ticking off every milestone this week, noting all of the “lasts” he is experiencing in his final of four Olympic Games. His last 200 butterfly. His last 200 medley. His last swim in the morning heats.

This represented his last individual Olympic final.

“I don’t even want to complain about going slower, or having a bad touch or finish,” Phelps said. “I’m not even going to say any of that. I’m just happy the last one was a win. This one was a bigger margin than the last two combined.”

Even while Phelps continued his week of revelry — Friday he even burst into a huge grin in the pool, a rarity for him after any victory — he said still couldn’t quite get his head around this finale.

“I thought it would hit me a lot harder than what it is right now,” he said. “A lot of those emotions really haven’t come through my brain this meet . . . I think I’m just kind of in meet mode.”

For USA Swimming — past, present and most certainly future — it has been a meet to remember.

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